Core Java Releated Quesstion

[pinakin raval]

What is the difference between the abstract class and the interface

[Shalini Chandel]

An Abstract class declares have at least one instance method that is declared abstract which will be implemented by the subclasses. An abstract class can have instance methods that implement a default behavior.

An Interface can only declare constants and instance methods, but cannot implement default behavior.

Hope this help...

Regards,
Shalini

[Akhilesh Trivedi]

further you can assume, an interface is a COMPLETE abstract class. :-)

[Jeroen Wenting]

no. In interface in Java has a somewhat similar role to a pure virtual class in C++ (though there are important (mainly philosophical) differences as well).

There's no such beast as a "complete virtual" class and interfaces aren't classes (even if they compile to .class files, probably because the JVM designers didn't want to introduce yet another file type).

[Mikalai Zaikin]

Originally posted by Shalini Chandel:
An Abstract class declares have at least one instance method that is declared abstract which will be implemented by the subclasses. An abstract class can have instance methods that implement a default behavior.

Wrong.

Abstract class :

1. May have no methods at all:

  
public abstract class A {
 
}

2. May have no abstract methods (all methods are concrete):

public abstract class A {
public static void main(String[] args) {
}
}

regards,
MZ

[Akhilesh Trivedi]

Originally posted by Jeroen Wenting:
no. In interface in Java has a somewhat similar role to a pure virtual class in C++ (though there are important (mainly philosophical) differences as well).

There's no such beast as a "complete virtual" class and interfaces aren't classes (even if they compile to .class files, probably because the JVM designers didn't want to introduce yet another file type).

interfaces aren't classes? Agreed Wenting. But I said you can assume them to be COMPLETE abstract classes. I dont want to talk of C++ or terms like "virtual" in an SCJP forum, the following link would speak what I meant...

http://www.google.co.in/search?biw=800&hl=en&q=%22interfaces+are+abstract+classes%22+java&btnG=Google+Search&meta=
[ June 28, 2005: Message edited by: Akhil Trivedi ]